1. Field of the Invention
The present invention relates to an electronic control unit and a system for the protection of vehicle occupants using a restraint system including a dual-stage airbag and/or seat belt pretensioner having both driver and passenger side firing circuits.
2. Description of the Related Art
U.S. Pat. No. 5,187,465 discloses a dual airbag restraint system having two firing circuits for independently operating a driver-side squib and a passenger-side squib.
Also known is a dual-stage airbag restraint system in which a single airbag is deployed in stages, initially on a driver side and subsequently on a passenger side. As illustrated in FIG. 9, the prior art dual-stage airbag control system is comprised of an electronic control unit 101 and a dual-stage firing module 102. ECU 101 has a first pair of transistors 104 and 105 having their source-drain paths connected in a first series circuit between the high and low voltage terminals of a DC voltage source 103 and a second pair of transistors 106 and 107 having their source-drain paths connected in a second series circuit between the high and low voltage terminals. In the first series circuit the squib 112 of the first-stage firing circuit is connected. In the second series circuit the squib 113 of the second-stage firing circuit is connected. All transistors are controlled by gate control signals supplied from a switching controller 120. Switching controller 120 receives an input voltage representing the impact on the passenger vehicle. When the input voltage exceeds a critical level, the switching controller 120 causes the transistors 104 and 105 to turn ON to fire the squib 112 so that the airbag is deployed on its driver side. Subsequently, the switching controller 120 enables the transistors 106 and 107 to turn ON, causing the squib 113 to deploy the airbag on its passenger side. However, two connector pins 108, 109 are required for activating the first firing circuit 112 and two connector pins 110, 111 are further required for activating the second firing circuit 113. Since it is desired that the number of channels for connecting the dual-stage firing module 102 to the ECU 101 be as small as possible to simplify the vehicle's harness, the prior art system is not satisfactory from the manufacturing viewpoint.
U.S. Pat. No. 6,744,820 discloses a communication system for connecting a master unit to slave units of an occupant protection system using frame messages asynchronously multiplexed on a pair of communication lines. Electrical energy and messages are transmitted from the master unit to a number of slave units by modulating the voltage of the electrical energy. Although the number of channels can be reduced, the components of the system are complex and expensive.